Compound semiconductors such as GaAs, InP and so on have been expected to be used as high speed devices because their electron mobility and saturation drift velocity are higher than Si (silicon). Already GaAs MESFET (Metal Semiconductor Field Effect Transistor) has been practically used.
Although superior properties were expected of InP, such superior properties in comparison with GaAs, InP have not been practically used for producing MESFET on account of high barrier height and difficulty in producing a Schottky junction with small reverse leakage current.
Conventionally, several attempts to interpose a thin insulating layer such as Al.sub.2 O.sub.3, SiO.sub.2 having a thickness of about 30 .ANG. between an InP and a gate electrode metal have been proposed in order to improve the barrier height of a Schottky diode made of InP.
However, such various attempts have provided only an InP Schottky diode with a barrier height .PHI. B of at its highest of 0.5 eV obtained from current-voltage characteristic, or large reverse leakage current. Further a conventional Schottky diode was possessed of poor properties such as an ideal factor n=1.5 to 2.0 representing completeness of the Schottky contact. The ideal factor n is deduced from the following equation representing the relationship between a forward current and voltage of the Schottky diode; ##EQU1## where, the saturation current Io is represented by following equation; ##EQU2## where, A represents the Richardson constant.
On the other hand, the general phenomena of semiconductor devices, the condition of the semiconductor surface remarkably influences characteristics of the semiconductor device. In a silicon semiconductor device, the density of interface trap density between Si and SiO.sub.2 layers is remarkably low and its insulating layer per se is stable so that good characteristics of a semiconductor device can be provided. However, a required insulating layer having a low interface trap density for a compound semiconductor has not yet been provided.
For example, various materials such as evaporated SiO and CVD-SiO.sub.2 (Chemical Vapor Deposition) have been studied for a long period of time in connection with use thereof as an insulating layer for the InP made MIS diode or MISFET. They do not possess a low interface trap density and a small current drift. In recent years, some attempts have been made to produce a special insulating layer (for example, AIPxOy) including the V-group elements by means of a thermal CVD method in order to control V-group elements.
In the insulating layer grown by using a hot CVD method, however, the surface of InP semiconductor should be exposed to high temperatures from 300.degree. to 450.degree. C. immediately prior to the formation of an insulating layer. This will possibly cause a decomposition of the InP semiconductor surface and vapor phosphorus thereby resulting in a problem for controlling the V-group elements. As a result, this method has not provided a desired insulating layer with an excellent interface property.
It is an object of the present invention to provide a method for producing an InP-made Schottky diode with a high barrier height and an excellent current-voltage characteristics.
Another object of the present invention is to provide a method for producing a semiconductor device including a III-V group (indium and/or phosphorus) compound semiconductor which ensures a decrease in the density of the state at the surface of the device, improves the capacitance-voltage characteristics of a MIS type diode, and provides a MISFET with a good performance.